This section provides background information related to the present disclosure which is not necessarily prior art.
Most current solar panels, including inorganic thin-film photovoltaics (PVs), are fabricated via complex processes using expensive semiconductor materials, and they are rigid and heavy with a dull, black appearance. The black color of the traditional PV panels is due to use of a thick semiconductor layer to absorb most incident light. Because of their non-aesthetically appealing appearance and weight, they are primarily installed on rooftops to minimize their negative impact on building appearance and aesthetics. As such, large surfaces and interiors of modern buildings are not efficiently utilized for potential electric power generation. This unattractive appearance limits the seamless integration with the interior as well as the exterior of existing architectures, such as facades, skylight, windows, and sidewalls. Thus, there is a strong demand to develop thin-film PVs that can offer design features, accompanying a variety of distinct colors.
Thus, inorganic thin-film solar panels have remained largely unexploited in creating various colors, which is primarily attributed to a photoactive layer having to be a few hundred nanometers thick. Such conventional inorganic thin-film solar cells require a minimum thickness of photoactive layers, which is mainly due to the doped regions forming an internal electric field in the active layer. For example, a photoactive layer of conventional thin-film amorphous silicon (a-Si) PV cells needs to be thick enough to accommodate the doped regions and intrinsic undoped layer in between. The doped layers are each at least 40 to about 50 nm thick to allow for proper photovoltaic operation. The doping in a-Si photoactive layer has been optimized over the last several decades to ensure that the intrinsic layer has a strong internal electric field for efficient charge extraction. In the doped regions of a-Si, photogenerated charges inevitably become recombined with the intended dopants, leading to substantial electric charge loss. However, ironically, the doped regions do not contribute to electric charge generation since photogenerated charges in doped a-Si are recombined by dopants, so-called defects. In addition, the inevitably thick a-Si active layer is subject to light-induced degradation, so that traditional a-Si solar cells have struggled to be implemented in practical use.
Integration of organic PVs with the color filters employing certain nanostructures has been previously proposed to simultaneously generate electric power and produce colors. However, an incident angle tolerance, one of the most important features, was not satisfactory. Even with the incorporation of any other plasmonic and photonic subwavelength grating based color filters, the incident angle dependent property is still a very challenging issue. Further, the organic based filters have not been desirable, as they suffer from degradation of the performance over time by longstanding ultraviolet illumination, heat, and chemical reactions. For example, organic photovoltaics are known to suffer from oxygen and moisture sensitivity and have short lifetimes. Further, these types of photovoltaics are also difficult to scale to practical large areas.
Because color filters have been used in a variety of display technologies as well as light emitting products, their integration with an ultra-thin a-Si photoactive layer would be desirable for colored photovoltaic panels. However, in practical applications, most nanostructure based plasmonic and photonic color filters have faced challenges in shifting a resonance, which occurs when light is incident upon the device at different angles of incidence. This resonance shift results in an undesirable color change, dramatically limiting the use of this type of filter. Therefore, there is a need to develop an incident angle robust color generating design for photovoltaic cells.